The present invention relates to a method and an apparatus for setting the outer diameter of a bladder of a tire forming drum, and more particularly to a method and apparatus for attaching a belt-shaped member to the outer circumferential surface of the bladder of the tire forming drum.
In building a tire, there is a step of winding a belt-shaped member made of a raw rubber around a forming drum to attach the member to the drum as shown in, for example, Japanese Patent Application Laid-open No. 63-95,939. In the attaching step using the apparatus disclosed in this Japanese Publication, the forward end of a belt-shaped member is held at a position on the outer circumferential surface of a forming drum made of a steel by means of a restraining jig, and then the forming drum is rotated to attach the trailing portion of the belt-shaped member on the outer circumferential surface of the drum successively. The restraining jig is provided with suction portions of magnets at both the ends and a sponge-like material at the center. As the magnets at both the ends of the jig are attracted to the forming drum made of the steel, the forward end of the belt-shaped member is held by the sponge-like material at the center of the jig.
Other than the drum made of a metal as described above, there are often used forming drums having air bags (bladders) made of rubbers which are filled with pressurized air to be inflated to predetermined outer diameters. In attaching a belt-shaped member to such a forming drum having such bladders, it has, in the past, been necessary to manually arrange belt-shaped members of a predetermined length around the bladders having outer circumferential surfaces tapered in their axial directions and to manually adjust the positions of the belt-shaped members on the bladders after filling pressurized air into the bladders to exhibit horizontal outer circumferential surfaces.
However, bladders often do not exhibit constant outer diameters when being inflated due to deterioration with age or the like. Therefore, if belt-shaped members are attached to such bladders in the manner according to the procedure disclosed in the Japanese Patent Application Laid-open No. 63-95,939, the joined lengths at the ends of the members unavoidably lie in a wide range. In such a prior art, accordingly, the belt-shaped members are previously formed into rings to have optimum joined lengths and then arranged around the bladders before being inflated. Thereafter, the belt-shaped members are formed into predetermined shapes by inflating the bladders as described above.
Before or during being inflated, however, the bladders have outer circumferential surfaces tapered in their axial directions, that is to say, outer diameters are different at their axial positions. Therefore, the ring-shaped members arranged around the bladders tend to move in their axial directions. Consequently, it has been required to manually adjust the members around the bladders into finally optimum positions as described above.